1. Field of the Invention
This invention relates to an improved process for producing benzylphthalazinone derivatives with a high yield.
2. Description of the Prior Art
Japanese Patent Publication No. 31154/1980 describes that the compound represented by the general formula [I]; ##STR4## wherein X is a halogen atom and R.sup.1 is a lower alkyl group, is suitable for use as an antihistaminic agent and discloses a process for preparing said compound utilizing the cyclic ammonium transition method. According to this conventional art, a crude final product can be obtained at an yield of at least 90%, which however contains a large quantity of by-products. If the target product is isolated from the crude product by crystallization, the yield will fall to 30% or lower.
For the reasons stated above, this conventional art is not satisfactory for commercial production.
Thus, there is a definite need in the art for a process for producing benzylphthalazinone derivatives (so-called "benzylphthalazone derivatives") with a high yield.
There is also a need in the art for a process for producing benzylphthalazinone derivatives with a high yield which does not require severe reaction conditions.